Method for estimating the quantity of polluting species in the exhaust gases of a compression-ignition engine, equipped with at least one catalyst for the selective reduction of nitrogen oxides.

Abstract

Method for estimating the quantity of polluting species in the exhaust gases of a motor vehicle equipped with a compression-ignition engine and at least one catalyst for selective reduction of nitrogen oxides, the estimation method making it possible to estimate the quantity of polluting species in the exhaust gases, in particular before a possible concentration sensor is hot enough to carry out measurements, comprising the following steps: a. identifying (1) the chemical reactions in the at least one selective reduction catalyst having the polluting species as reactant or product, b. determining (2) the reaction rates of each identified chemical reaction, c. carrying out (3) a mass balance in the at least one catalyst for selective reduction of nitrogen oxides considered as an open system, for each polluting species, and d.(4) the quantity of polluting species in the exhaust gases is determined based on the mass balance. Figure for abstract: [Fig 1].

Description

Title of the invention: Method for estimating the quantity of polluting species in the exhaust gases of a compression-ignition engine, equipped with at least one catalyst for the selective reduction of nitrogen oxides. Technical field

[0001] The technical field of the invention is the estimation of the polluting species produced by a compression ignition engine, and more precisely, the polluting species produced by a compression ignition engine equipped with at least one catalyst for the selective reduction of nitrogen oxides (also called SCR, from the acronym in English for: "Selective Catalytic Reduction"). Previous techniques

[0002] The new Euro 7 / VII standard, which will come into force from 2025, requires a reduction in pollutant emissions, compared to the current standard (Euro 6e), for vehicles sold in Europe.

[0003] Among the polluting emissions, the Euro7 / VII standard is particularly strict with regard to emissions of nitrogen oxides NOX and ammonia Ml;.

[0004] Among these gases, the particularities of NO2 and nitrogen dioxide NO2 are noteworthy. Nitrogen dioxide NO2 is a toxic gas that produces inflammation of the respiratory tract and contributes to the formation of acid rain. Ammonia NH3 contributes to the formation of secondary particles, associated with cardiovascular and respiratory diseases, and is harmful to aquatic environments.

[0005] The Euro 7 / VII standard includes an obligation for on-board diagnostics OBM (acronym for "On-Board Monitoring"). It will be mandatory to monitor, on each journey made by the vehicle, the quantity of nitrogen oxides NOX (essentially nitrogen monoxide NO and nitrogen dioxide NO2) and the quantity of ammonia NH3 emitted from the exhaust. The vehicle will have to transmit these values ​​not only via the on-board diagnostics OBD (acronym for "On-Board Diagnostic") socket but also via wireless communication OTA (acronym for "over the air") to a dedicated platform.

[0006] If the emissions of nitrogen oxides NOX or ammonia NH3 exceed a predefined limit, constructed by multiplying the regulatory threshold of the species considered by a predetermined factor greater than 1, called the conformity factor CF, then the vehicle must alert the driver by means of warning lights on the dashboard and require the vehicle to be repaired via engine torque and vehicle speed limitations, or even by prohibiting starting.

[0007] In other words, if the emissions are higher than, for example, 1.5 or 2 times more than predetermined thresholds, generally obtained during the approval of the vehicle, calculated over a number of valid journeys, the alert must be given.

[0008] In order to determine these values, a concentration sensor for determining the concentration of these pollutants in the exhaust gases must be provided in vehicles aiming to obtain vehicle approval. An on-board diagnostic system for the sensor is also required.

[0009] However, existing types of sensors are not capable of taking a measurement until their sensitive element has reached a threshold temperature, known as the operating temperature. The temperature rise of the sensor can last up to 900 seconds from the start of driving for compression ignition vehicles (diesel type).

[0010] It thus appears that it is not possible to satisfy the Euro 7 standard with the existing sensors alone due to the absence of measurement up to 900 seconds after the start of driving.

[0011] There is a need for determining the emissions of nitrogen oxides and ammonia at the exhaust outlet of a compression ignition engine, before the operating temperature is reached by the sensor for measuring these pollutants.

[0012] In the state of the prior art, many documents deal with the estimation of the quantity of nitrogen oxides.

[0013] We can cite in particular documents US8225595, US20170044962, US9771846, US9304061, EP2832965, EP2910758 and EP3819483 dealing with the specific case of diesel engines, which does not apply to the present problem.

[0014] Mention may also be made of documents US 11028753, JP2009287410, US2008 / 108212 and WO2016 / 159019Al describing models for determining the quantity of nitrogen oxides but only at the engine outlet, and not at the exhaust outlet after the post-treatment device(s).

[0015] Documents EP3736418 and EP3956549 disclose models for estimating these emissions based on the measurement of sensors. These documents are inapplicable here due to the impossibility of carrying out a measurement until the sensor has reached its operating temperature.

[0016] The technical problem is therefore not solved by the state of the prior art. Statement of the invention

[0017] The subject of the invention is a method for estimating the quantity of polluting species in the exhaust gases of a motor vehicle equipped with a compression ignition engine, and at least one first selective reduction catalyst. nitrogen oxides, the estimation method making it possible to estimate the quantity of polluting species in the exhaust gases, in particular before any concentration sensor is hot enough to carry out measurements, the method comprising the following steps:

[0018] the chemical reactions involved in the first catalyst for selective reduction of nitrogen oxides having as reactant or product the polluting species whose quantity in the exhaust gases must be estimated are identified,

[0019] the reaction rates of each identified chemical reaction are determined,

[0020] a mass balance is carried out in the first catalyst for the selective reduction of nitrogen oxides considered as an open system, for each of the polluting species whose quantity must be determined, and

[0021] the quantity of polluting species in the exhaust gases is determined based on the mass balance.

[0022] The polluting species can be nitrogen monoxide and ammonia, the estimation method can then comprise the following steps:

[0023] the temperature in the first catalyst for selective reduction of nitrogen oxides, the flow rate in the first catalyst for selective reduction of nitrogen oxides, the quantity of ammonia entering the first catalyst for selective reduction of nitrogen oxides, the speed and the torque of the compression ignition engine are determined,

[0024] the molar fraction of nitrogen oxide in the gases leaving the compression ignition engine is determined by applying a first map depending on the speed and the estimated torque of the engine,

[0025] the molar fraction of nitrogen oxides in the gases leaving the first catalyst for selective reduction of nitrogen oxides, arranged downstream of the compression-ignition engine, is determined as a function of the molar fraction of nitrogen oxides produced by the engine, and of the flow rate in the first catalyst for selective reduction of nitrogen oxides and, as well as of a second 1D map dependent on the temperature in the first catalyst for selective reduction of nitrogen oxides and of a third 1D map dependent on the flow rate in the first catalyst for selective reduction of nitrogen oxides,

[0026] the molar fraction of ammonia in the gases leaving the first catalyst for selective reduction of nitrogen oxides is also determined, as a function of a fourth 1D map dependent on the temperature in the first catalyst for selective reduction of nitrogen oxides and the molar fraction of nitrogen oxides in the gases emitted by the compression ignition engine.

[0027] When, as is frequently the case, the motor vehicle is equipped with a second catalyst for selective reduction of nitrogen oxides downstream of the first catalyst for the selective reduction of nitrogen oxides, the process may comprise the following steps:

[0028] the molar fraction of ammonia in the gases leaving the second catalyst for selective reduction of nitrogen oxides is determined, as a function of a fifth 1D map dependent on the temperature in the second catalyst for selective reduction of nitrogen oxides and as a function of the value of the number of ammonia adsorption sites,

[0029] the molar fraction of nitrogen monoxide in the gases leaving the second catalyst for selective reduction of nitrogen oxides is determined as a function of the molar fraction of nitrogen monoxide in the gases leaving the first catalyst for selective reduction of nitrogen oxides, and of the flow rate in the second catalyst for selective reduction of nitrogen oxides, as well as of a sixth 1D map dependent on the temperature in the second catalyst for selective reduction of nitrogen oxides and of a seventh 1D map dependent on the flow rate in the second catalyst for selective reduction of nitrogen oxides.

[0030] The maps can be calibrated based on measurements made during tests.

[0031] The polluting species may be carbon dioxide, carbon monoxide, hydrocarbons, ammonia, nitric oxide, nitrogen dioxide or nitrous oxide.

[0032] The invention also relates to a motor vehicle equipped with an estimation system configured so as to carry out the estimation method as described above, in particular within an on-board diagnosis.

[0033] The motor vehicle may further comprise a circuit for partial recirculation of the exhaust gases at the intake. Brief description of the drawings

[0034] Other aims, characteristics and advantages of the invention will appear on reading the following description, given solely by way of non-limiting example and made with reference to the appended drawings in which:

[0035] - Figure [Fig.l] illustrates the main steps of a method for estimating the quantity of polluting species in exhaust gases. Detailed description

[0036] We recall the following notions specific to the determination of reaction rates in general in a given system, which can be open or closed. We pose the following generic chemical reaction:

[0037] aA + bB cC + dD

[0038] with

[0039] a,b,c,d: stoichiometric coefficients

[0040] A,B: reactants of the reaction

[0041] C,D: products of the reaction.

[0042] We define the speed v of this chemical reaction in moles per unit of time:

[0043] [Eq. 1]

[0044] v = Vobf(T) • [Af[B]p

[0045] With:

[0046] Vol: the system volume,

[0047] / (jj: a function of the temperature T of the system,

[0048] [A], [B]: the volume concentrations of reactants A and B respectively,

[0049] A, [3: the powers applied to these concentrations.

[0050] The function f is often modeled by an Arrhenius law:

[0051] [Eq. 2]

[0052] f(T) =keEaAr

[0053] where:

[0054] k: a pre-exponential factor of the reaction

[0055] Ea: the activation energy of the reaction

[0056] R: the universal constant of ideal gases (-8.3145 J / K)

[0057] T: the reaction temperature, in Kelvin

[0058] However, this expression only provides two degrees of freedom, the pre-exponential factor k and the activation energy Ea, to adjust it. Experimentally, the dependence of the reaction rate on temperature can have a more complex form. In the remainder of this description, the more generic form / (T) will therefore be used.

[0059] If the system is open, as is the case with a selective nitrogen oxide reduction (SCR) catalyst mounted in the exhaust of a compression ignition engine, the function f may also have a dependence on the axial gas velocity, obtained as the gas volume flow rate divided by the cross-sectional area of ​​the system. For a constant cross-section, the equation [Eq. 1] can be rewritten:

[0060] [Eq. 3]

[0061] v^Vol-f(T,QY[A}a[B]p

[0062] For an open system, the mass balance for a species A, in moles, is written:

[0063] [Eq. 4]

[0064] x x yy dt An ^out Axit prod A Aj cons AA

[0065] With:

[0066]

[0067]

[0068]

[0069]

[0070]

[0071]

[0072]

[0073]

[0074]

[0075]

[0076]

[0077]

[0078]

[0079]

[0080]

[0081]

[0082]

[0083]

[0084]

[0085] dnA: Variation per unit of time of the number of moles of species A in the dt system Q: Molar flow rate of gases entering the system : Mole fraction of species A in the gases entering the system Q: Molar flow rate of gases leaving the system : Mole fraction of species A in the gases leaving the system Number of moles of species A generated per second by reactions where species A is a product V v: Number of moles of species A consumed per second by AN consumers reactions where species A is a reactant It should be remembered that an SCR fitted to the exhaust of a compression ignition engine is a gas post-treatment device which aims to reduce the nitrogen oxides contained in the exhaust gases received from the engine into harmless molecules under the action of ammonia present in the SCR and coming from a urea-based solution (Adblue®) which is injected upstream of said catalyst. In an SCR, especially a first SCR, the main reactions involving nitrogen monoxide NO and ammonia NH3 are as follows: Adsorption reaction of ammonia NH3 in an ammonia adsorption site noted as V, NH3 + as _^NH3_as Desorption reaction of ammonia NH3 from an ammonia adsorption site denoted as V2 NH3~as _^NH3 + as- Reduction of nitric oxide by adsorbed ammonia NH3_as NH3_as + NO + jO2 N2 + ^H2O + as Reduction of nitric oxide NO and nitrogen dioxide NO2 by adsorbed ammonia NH3_as I 1 ^4 / NH3_as +jNO + lNO2 2 N2 + 3j 2 H2O + as Reduction of nitrogen dioxide NO2 by adsorbed ammonia NH3_as NH3_as + ^NO2 ^N2 + 3 / 2^0 +as Oxidation of adsorbed ammonia NH3_as to nitrogen N2

[0086]

[0087]

[0088]

[0089]

[0090]

[0091]

[0092]

[0093]

[0094]

[0095]

[0096]

[0097]

[0098]

[0099]

[0100]

[0101] V6 / NH3_as + % O2 ¥2 N2 + 3 / 2 H2O + as In this set of reactions, the reactants NO, NO2, NH3 and O2 are in the gaseous state. With : v^mol / s] = vjmol / s] = Vol • f2(T, Q) • [VH3_asJz2 vjmol / s] = Vobf / T,e)^ff3_asrWxf3 \Jmol / s] = Vol • f 4(T, Q) • [NH3~ asfW / vjmol / s] = Vol<5(T,2)-[VH3_asrW^ vjmol / s] = Vol • f6(T, g)• And : «v, «io and Pp, : coefficients The internal temperature of the catalyst T and the exhaust gas flow rate Q through the catalyst are determined, that is to say either measured using sensors or estimated by an electronic control unit of the motor vehicle, and are subsequently considered as input data. In a theoretical approach such as presented above, it is necessary to calibrate as many two-dimensional functions, , that of reactions considered. In the case presented above, six two-dimensional functions are to be calibrated for only the reactions affecting nitrogen monoxide NO and ammonia It is also necessary to estimate, in addition, the concentrations of the rest of the reactants involved in each of the reactions identified above (here dioxygen O2) which will in turn be determined via new reaction schemes. In addition, it is necessary to determine the üp P parameters for each of these new reactions. It thus appears that the determination and calibration of an exact model taking into account all the reactions affecting the concentration of nitrogen monoxide NO and ammonia NH3 becomes very complex. Indeed, there are many more functions to calibrate than observed phenomena (i.e. the quantities of nitrogen monoxide NO and ammonia NH3 at the outlet of the SCR in the system considered here) and different solutions would be possible, all correctly adjusting the experimental results, but without the certainty that one of them correctly describes the physical and chemical phenomena involved.

[0102] Furthermore, the very high dynamic nature of the reactions would require choosing very small sampling steps (due to the stability of the calculations), which would make it difficult to integrate this solution into a computer, which would be overloaded.

[0103] In the method detailed below, a certain number of hypotheses will be made in order to resolve these two problems and arrive at a solution which is both easy to calibrate and to embed in a computer.

[0104] The following assumptions and considerations apply identically regardless of the type of emission to be determined. In the present case, they will be described for a system comprising the compression ignition engine and at least one SCR, and for which we seek to estimate the quantities emitted of nitrogen monoxide NO and ammonia NH3.

[0105] The system is considered homogeneous in space, that is to say that the temperature and the concentrations are the same at all points of the system considered. In other words, the model is a 0D model. The molar fractions inside and at the exit of the system are identical and it is therefore possible to write:

[0106] [Eq. 5]

[0107] _ nvn ,v .y V ^in ^out A prod AA^ cons A \

[0108] The system is considered quasi-stationary. The variations in the number of moles of the gaseous species are instantaneous. Furthermore, the inlet flow rate is very close to that at the outlet:

[0109] [Eq.6BV Q^Q

[0110] Based on these assumptions, the following equations are set:

[0111] For a species A such as for example nitrogen monoxide NO, the variation in the number of moles in the system being considered instantaneous, the differential term is cancelled:

[0112] [Eq. 7]

[0113] o = Q • Xy - Q • XA + R , Âv - E (Gas Species A) A proa A Aj cous y

[0114] For a non-gaseous species A such as ammonia NH3 stored in the SCR, the differential term is taken into account:

[0115] [Eq. 8]

[0116] nY Y (Non-gaseous Species A) dt Am A prod AA^ cons A

[0117] The dynamics of the gas-phase species has been removed, which has the effect of transforming the differential equations into algebraic equations.

[0118] By definition, the concentration of species A is written:

[0119] [Eq. 9]

[0133]

[0120] । Â -, _ [ÆJ - vd - vd

[0121] With: XA the molar fraction of species A in all the species present in the SCR, and n the total quantity of species in the catalyst, in moles.

[0122] For species in the gas phase, the ideal gas law is applied.

[0123] [Eq. 10]

[0124] PVol = nRT

[0125] We can then reformulate the equation [Eq. 9] as follows:

[0126] [Eq. 11]

[0127] [A]-XaP!(RT)

[0128] By neglecting the effect of pressure variations in the reaction rates (i.e. by considering P substantially constant) in a new generic function Q), we can write the following equations:

[0129] [Eq. 12] [OBO] y[me / s] = flight ■ g(T, Q) • X / x /

[0131] with v: the reaction rate for a two-reactant reaction in gas form

[0132] [Eq. 13] mol / s] = Vol • g^T, çj ■

[0134] with v: the reaction rate for a reaction comprising a single reactant in gas form.

[0135] For each reaction rate, only the dependence on a single gaseous reactant is retained, the one considered to be limiting. The other reactant is not taken into account if it is also in the gaseous state or if it is considered in excess. We then reformulate equations [Eq. 12] and [Eq. 13] as follows:

[0136] [Eq. 14] [0B7] ^molI s] = Vol. g(T> q) . X /

[0138] with v: the reaction rate for a reaction with two reactants in gas form

[0139] [Eq. 15] 101401 v[mol / s] = Vol^T.Qj.X / t-^)'

[0141] with v: the reaction rate for a reaction comprising a single reactant in gas form.

[0142] For simplification, we set a — fi = L

[0143] We therefore obtain: [°144] ^nwi 1^ = yoi. g(T, q) . xA , A limiting gaseous reactant [014-5] ^moljs] = g{T,Q)-XA. n^, A limiting gaseous reactant, B non-gaseous

[0346] ^molfs] = ^r, Q) • B non-azose reagent

[0147]

[0148] The NOX (gaseous) will be consumed by the reactions with the NH3 stored in the SCR:

[0149] [Eq. 16]

[0150] 0 = Q ■ Xnox - Q ■ XNO - gNO (T, Q) ■ X^o • as

[0151] NH3 (gaseous) can be adsorbed or desorbed:

[0152] [Eq. XNH3.nQ-XNh3 +gdNH( T, Q) n^H^as-Vol -ga nh^T,Q) XNh3

[0153] The adsorbed ammonia NH3_as can vary due to adsorption / desorption phenomena and can be consumed by reactions with NOX and by oxidation with O2:

[0154] [Eq. 18]

[0155] = Vol-gaJllh(T,Q)- Xm,-g^^ (T,Q)- nm3jl-(T,Q)-

[0156] The combination of the equations obtained with the assumptions made above makes it possible to write the balance equations in a linear form with regard to the mole fractions X, which can be obtained explicitly, and therefore without the need for an iterative calculation, making it possible to use a calculation step 100 to 1000 times larger in the iterative simulations by exact model, with a negligible loss in precision.

[0157] The mole fractions XN0 and Xnh3 can be isolated from the first two equations and obtained explicitly.

[0158] Adsorption phenomena are considered immediate: any species A entering or produced in the system is stored instantly. Instead of calibrating an adsorption rate and a desorption rate, only the desorption rate is taken into account.

[0159] [Eq. 19]

[0160] Vol • ga NH3(T,Q)-XNh3=Q ■ Xnh3.k

[0161] and therefore:

[0162] [Eq. 20]

[0163] 0 = Q • Xnox.k - Q • XNOx - gcNO^ (T,Q) • XNOx ■

[0164] [Eq. 21]

[0165] 0 = - Q • XNh3 + gd NH (T,Q) • nNH^as

[0166] [Eq. 22]

[0167] = q. - gd NHi (T, Q) • nNH3as - gcjm< (T, Q)X NOT • nNH^ - geJVHiJa (T,Q) • nNH^s

[0168] The system is thus reduced to three functions to be calibrated, noted ^c_NO^ agg^NHv

[0169] The following assumptions apply to the specific case of nitrogen monoxide NO and ammonia NH3 emissions. The choice of these assumptions was made in response to purely empirical or simplification criteria.

[0170] The molar fractions of nitrogen oxide NO and ammonia NH3 can be written as follows:

[0171] [Eq. 23]

[0172] A NOX Q+gc ^T.Qyn^H.^

[0173] [Eq. 24]

[0174] v gd_NH.(T,Q)nNH^ ANHj~ q

[0175] [Eq. 25]

[0176] =q,Xnh -gd H (T,Q) -XNOx-nNH3n^

[0177] Empirically, we pose:

[0178] [Eq. 26]

[0179] ge XOx(T, Q) Kgc NOx T(T) gc NOx_q(Q)

[0180] [Eq. 27]

[0181] nh^os^ Ô) as q(Q)

[0182] This simplification is based on experience, in fact the gc functions and act by modulating the functions gc NO^T( T) and gc NH as t^T) respectively. Thus, for low flow rates, gc Xqx^(Q) and gc NH as are equal to unity, but their value decreases as the flow rate increases.

[0183] This transforms a two-dimensional function into two one-dimensional functions, easier to calibrate and with less risk of extrapolation.

[0184] Empirically, we pose:

[0185] [Eq. 28]

[0186] ■ T, Q) “Q • gd T)

[0187] Indeed, experimentally, at iso-temperature, we observe a variation of the gd_NH3 function proportional to the flow rate passing through the SCR.

[0188] Equations [Eq. 23] and [Eq. 25] can then be rewritten as follows:

[0189] [Eq. 29]

[0190] Y__________

[0191] [Eq. 30]

[0192] %NH3~ gj NH M-NH^as

[0193] [Eq. 31]

[0194] <ü " 0                    ' anltno, ’ sc         '^nor’                     ^e-nli^us^

[0195] At this stage, we have the set of equations [Eq. 29] [Eq. 30] and [Eq. 31] in order to determine the quantity of nitrogen monoxide NO and ammonia NH3 at the outlet of each SCR.

[0196] The ease of calibration (over a few dynamic cycles carried out on a test bench) as well as the ease of integration into a computer due to the few resources required, make this process an ideal candidate for application in the context of on-board OBM monitoring in a Euro 7 / VII standardized vehicle.

[0197] The physical approach used in this invention is advantageous compared to other statistical or machine learning approaches due to its explainability and the need for fewer tests (generally quite expensive) for its calibration. Indeed, the contribution of theory to the model makes it possible to better predict the response of the system in areas where there would be less learning data. The area of ​​use of the system is better covered.

[0198] Finally, the simplifications made to the model facilitate the calibration task with a negligible loss of precision.

[0199] The steps of the estimation method are notably executed by a calculation means, included in the on-board electronic computer of the vehicle or in a specific computer. The computer comprises in all cases at least one processor, a memory and means of communication with the rest of the vehicle and notably the sensors and estimation means, via a wired network, notably of the CAN type or a wireless network.

[0200] The nitrogen oxides NOX and the ammonia NH3 at the outlet of each SCR are admitted at the inlet of the SCR located downstream. In particular, when the engine is equipped with two SCRs in series, the nitrogen oxides NOX and the ammonia NH3 from the first SCR are admitted at the inlet of the second SCR.

[0201] The estimation process illustrated by figure [Fig. 1] comprises four main steps.

[0202] A first step 1 of measurement and estimation.

[0203] A second step 2 of estimating the emissions at the outlet of the compression ignition engine.

[0204] A third step 3 of estimating the emissions at the output of at least one first SCR.

[0205] A fourth step 4 of estimating the emissions at the output of a second SCR.

[0206] Nitrogen oxides NOX are formed at very high temperatures in the combustion chamber, when the oxygen O2 in the ambient air is able to react with nitrogen N2. For a compression ignition engine, this mainly involves the formation of nitrogen monoxide NO, but which can then be transformed into nitrogen dioxide NO2 with the ozone O. in the ambient air.

[0207] Ammonia NH3 is not formed in the engine but in the SCR, as a secondary product, from other combustion products such as nitrogen monoxide NO and dihydrogen H2. It will therefore not be estimated in this step.

[0208] The concentration of nitrogen oxides NOX at the engine outlet (in ppm) is determined as a function of the speed and torque estimated by the computer. This function can be given in the form of 2D maps.

[0209] A 2D map can be provided for each combustion mode of the engine, in particular a specific map can be provided during the regeneration phases of the post-treatment system or even a specific map during the heating phases.

[0210] Indeed, an SCR must be heated to reach a threshold temperature from which it has a predetermined minimum treatment efficiency. This temperature is generally reached by degrading the combustion efficiency of the engine, for example by delayed fuel injection.

[0211] Taking into account other variables, such as the partial exhaust gas recirculation rate EGR (English acronym for “Exhaust Gas Recirculation”) or the richness X, which are taken into account in part via the engine operating point (rotation speed / load), the combustion mode (for a given engine setting) or the characteristics of their regulation, is therefore not obligatory.

[0212] In the application case described here, a 1D mapping dependent on the estimated torque is preferred. Indeed, such a 1D mapping is simpler to calibrate, reduces the risk of extrapolation of the model and makes it possible to maintain sufficient cycle accuracy.

[0213] The nitrogen oxides NOX generated by the compression ignition engine are admitted into the first SCR in order to reduce them.

[0214] The reduction achieved is not total, and nitrogen oxides NOX are still present at the outlet of the first SCR. The residual nitrogen oxides NOX are then possibly admitted into a second SCR. This second SCR then achieves a reduction of the residual nitrogen oxides NOX.

[0215] The method for estimating the quantities of nitrogen monoxide NO and ammonia NH3 in the pollutant emissions of a vehicle equipped with an ignition engine by compression and an exhaust line with at least one first SCR according to the invention comprises the steps presented below.

[0216] In a particular case, the compression ignition engine may also have other features, in particular a partial exhaust gas recirculation circuit at the EGR intake.

[0217] The method for estimating the quantity of nitrogen monoxide and ammonia in the exhaust gases of a motor vehicle equipped with at least a first SCR is illustrated by figure [Fig.l] and comprises the following steps:

[0218] During a first step 1, the temperature in the first SCR, the flow rate in the first SCR, the speed and the torque of the compression ignition engine are measured or estimated.

[0219] During a second step 2, the molar fraction of nitrogen monoxide in the gases leaving the compression ignition engine is determined by applying a map depending on the speed and the estimated torque of the engine forming a first map.

[0220] During a third step 3, the molar fraction of nitrogen monoxide in the gases leaving the first SCR, arranged downstream of the compression ignition engine, is determined by applying the equation [Eq. 29], depending on the molar fraction of nitrogen monoxide produced by the engine and the flow rate in the first SCR, as well as a 1D map (gc y) dependent on the temperature in the first SCR forming a second map, and a 1D map (gc Q) dependent on the flow rate in the first SCR forming a third map. The molar fraction of ammonia in the gases leaving the first SCR is also determined by applying the equation [Eq. 30], a function of a map ( / \) dependent on the temperature in the first compression-ignition SCR. Said mapping (gdNH^ forms a fourth mapping.

[0221] When the motor vehicle is equipped with a second SCR downstream of the first SCR, the method continues with a fourth step 4.

[0222] During this fourth step 4, the molar fraction of ammonia in the gases leaving the second SCR is determined, by applying the same equation [Eq. 30] applied for the first SCR, a function of the mapping (¾ depending on the temperature and the flow rate in the second SCR.

[0223] The molar fraction of nitrogen monoxide in the gases leaving the second SCR is determined by applying the equation [Eq. 29], depending on the molar fraction of nitrogen monoxide in the gases leaving the first SCR, the flow rate and the volume of the second SCR, as well as a 1D map (§c_NOx_2_t) depending of the temperature in the second SCR forming a sixth map and a 1D map (Sc nox2 q) dependent on the flow rate in the second SCR forming a seventh map.

[0224] The model ([Eq. 29], [Eq. 30] and [Eq. 31]) makes it possible to describe in a simplified but reliable manner the generation and catalysis of pollutant emissions in a motor vehicle equipped with a compression ignition engine and at least a first SCR, and where appropriate (frequently) equipped with a second SCR.

[0225] In order to use this model, the following functions must be calibrated:

[0226] - 2D mapping as a function of the engine speed and estimated torque, giving the molar fraction of NOX at engine outlet, by combustion mode and by fuel type,

[0227] - the functions involved in determining the molar fraction of NOX in output of each SCR ([Eq. 29]),

[0228] - the functions involved in determining the number of moles of adsorbed NH3 ([Eq. 31]),

[0229] - the functions involved in determining the molar fraction of NH3 in output of an SCR ([Eq. 30]).

[0230] In other words, a (2D) map is to be calibrated for NOX emissions at the engine outlet in addition to the maps used to determine NOX and NH3 emissions at the SCR outlet (Scj^qx and Sd-NH^T)-

[0231] To carry out this calibration, dynamic tests are carried out covering the combustion modes, the engine field (rotation speed / torque), the flow rates and the temperatures in the at least one SCR, which may be observed during road use by the end customer.

[0232] To carry out such a calibration, the following acquisitions are carried out, in particular at an acquisition frequency of 10 Hz:

[0233] Engine output emissions: NOX

[0234] Emissions downstream of first SCR: NOX

[0235] Exhaust emissions: NOX, NH3

[0236] Internal temperatures in each SCR

[0237] Estimated speed and torque

[0238] Flow rate of NH3 injected into each SCR (by injection of Adblue®)

[0239] Combustion mode information

[0240] Flow rate through each SCR.

[0241] The model is calibrated for a given technical definition, SCR aging status, ECU calibration, and ambient conditions (temperature, pressure, humidity).

[0242] Based on the acquisitions made, the calibration is broken down into three stages:

[0243] Calibration of the quantity of nitrogen oxides NOX at the engine outlet,

[0244] Calibration of the quantity of nitrogen oxides NOX and the quantity of ammonia NH3 at the output of the first SCR, and

[0245] Calibration of the quantity of nitrogen oxides NOX and the quantity of ammonia NH3 at the outlet of the second SCR (if present).

[0246] As seen above, the quantity of nitrogen oxides NOX generated by the engine can be determined based on a two-dimensional map depending on the estimated torque and the rotational speed of the engine.

[0247] According to the embodiments, a 2D map is provided for each combustion mode of the engine.

[0248] To construct each map, the quantity of nitrogen oxides NOX [ppm] is determined by measurement as a function of the inputs, i.e., in the case of the example application, the indicated engine torque. The breakdown of this map is quite fine, in particular with a step of 10 Nm for the torque in a 2D map.

[0249] Several methods are possible to determine and complete the values ​​of the mapping around the measured values. These include the use of a neural network or a Gaussian process type model, for which a learning process is carried out on the measurements of the mapping.

[0250] This is a static model calibrated on dynamic cycles, consequently the measurement of nitrogen oxides NOX at the engine output must be well synchronized beforehand with the engine events used.

[0251] The expression obtained ([Eq. 29]) to calculate the molar fraction of nitrogen monoxide NO at the outlet of the SCR is applied indifferently to each SCR present. Only the origin and the quantity of the pollutants received at the inlet, the flow rate, the temperature and the volume change depending on whether it is the first or the second SCR.

[0252] When equation [Eq. 29] is applied to the first SCR, the value Xnos corresponds to the molar fraction of NOX in the gases leaving the engine and calculated in the first step of the process and X^q is the molar fraction of NOX in the gases leaving the first SCR.

[0253] In the present case, Q designates the flow rate passing through the first SCR (including the low pressure EGR if necessary) and T the internal temperature of the first SCR (homogeneous if a 0D model has been considered).

[0254] The ge NO etgc yo functions are then presented in the form of 1D maps. During calibration, these functions are adjusted or determined, in particular through mathematical modeling based on a sample of values ​​obtained during bench tests.

[0255] The function g^ w T) can be adjusted independently of the function gc NO for small flow rates, the function gc NO g( Ô) taking a value equal to 1 in such cases.

[0256] For high flow rates, the function g^ Q) takes values ​​lower than 1, in order to account for the efficiency losses in the treatment of nitrogen oxides NOX.

[0257] The molar fraction of ammonia NH3 at the outlet of the first SCR is given by the equation [Eq. 30] and the equation [Eq. 31] in which %NOin represents the molar fraction of nitrogen oxides NOX leaving the engine, calculated in the first step and represents the molar fraction of ammonia NH 3 at the outlet of the first SCR.

[0258] The function determined by bench measurements.

[0259] The molar fraction of nitrogen monoxide NO at the outlet of the second SCR is calculated with an expression similar to that used for the first SCR ([Eq. 29]) modified to take into account the gases coming from the first SCR:

[0260] [Eq. 32]

[0261] v Q_2+gc ^2 ^^ge ^

[0262] The variables are:

[0263] : molar fraction of nitrogen oxides NOX leaving the first SCR

[0264] Q_2: flow rate through the second SCR

[0265] T_2: internal temperature of the second SCR

[0266] -Vvo, 2: molar fraction of nitrogen oxides NOX at the outlet of the second SCR

[0267] The method for calibrating gc functions No t(T and Q_2) for the second SCR is identical to that used to calibrate the functions and S^no^q(Q) for the first SCR.

[0268] The production of ammonia NH3 in the second SCR only takes into account the adsorption and desorption phenomena, described by the equation [Eq. 33] below, adapted from the equation [Eq. 29] to take into account the admitted gases coming from the first SCR:

[0269] [Eq. 33]

[0270] XnhJI Sj NH ' ^NHy_as

[0271] [Eq. 34]

[0273] Where:

[0274] : molar fraction of NH3 leaving the first SCR and calculated in step previous.

[0275] HNH^as; number of moles of NH3 stored in the second SCR.

[0276] 2: molar fraction of NH3 at the outlet of the second SCR.

[0277] The function £d nh , t is determined from values ​​measured on the bench. It has a zero value until the temperature reaches a predetermined value reflecting the storage by adsorption of ammonia NH3, then an increase reflecting the release by desorption of the stored ammonia NH3.

[0278] The invention has been described above in the context of estimating the quantities produced of nitrogen oxides NOX and ammonia NH3. Nevertheless, the invention can be adapted to reactions involving other species as products and as reactants, in particular carbon dioxide CO2, carbon monoxide CO, hydrocarbons HC, nitrogen dioxide NO2 or nitrous oxide N2O,

Claims

Claims

1. Method for estimating the quantity of polluting species in the exhaust gases of a motor vehicle equipped with a compression-ignition engine and at least one first catalyst for selective reduction of nitrogen oxides, the estimation method making it possible to estimate the quantity of polluting species in the exhaust gases, in particular before a possible concentration sensor is sufficiently hot to carry out measurements, the method comprising the following steps: a. the chemical reactions involved in the first catalyst for the selective reduction of nitrogen oxides having as reactant or product the polluting species whose quantity in the exhaust gases must be estimated are identified, b. the reaction rates of each identified chemical reaction are determined, c. a mass balance is carried out in the first catalyst for the selective reduction of nitrogen oxides considered as an open system, for each of the polluting species whose quantity must be determined, and d. the quantity of polluting species in the exhaust gases is determined based on the mass balance.

2. The estimation method of claim 1, wherein the polluting species are nitrogen monoxide and ammonia, the estimation method comprising the following steps: a. the temperature in the first selective nitrogen oxide reduction catalyst, the flow rate in the first selective nitrogen oxide reduction catalyst, the quantity of ammonia entering the first selective nitrogen oxide reduction catalyst, the speed and torque of the compression-ignition engine are determined, b. the molar fraction of nitrogen monoxide in the gases leaving the compression-ignition engine are determined by applying a first map depending on the speed and the estimated torque of the engine,

3. c. the molar fraction of nitrogen oxides in the gases leaving the first selective nitrogen oxide reduction catalyst, arranged downstream of the compression-ignition engine, is determined as a function of the molar fraction of nitrogen monoxide produced by the engine and the flow rate in the first selective nitrogen oxide reduction catalyst, as well as a second 1D map dependent on the temperature in the first selective nitrogen oxide reduction catalyst and a third 1D map dependent on the flow rate in the first selective nitrogen oxide reduction catalyst, d. the molar fraction of ammonia in the gases leaving the first catalyst for selective reduction of nitrogen oxides is also determined, based on a fourth 1D map dependent on the temperature in the first catalyst for selective reduction of nitrogen oxides and the molar fraction of nitrogen oxides in the gases emitted by the compression-ignition engine. Estimation method according to claim 2, wherein, when the motor vehicle is equipped with a second catalyst for selective reduction of nitrogen oxides downstream of the first catalyst for selective reduction of nitrogen oxides, the method comprises the following steps: a. the molar fraction of ammonia in the gases leaving a second catalyst for the selective reduction of nitrogen oxides is determined, based on a fifth 1D map dependent on the temperature in the second catalyst for the selective reduction of nitrogen oxides and based on the value of the number of ammonia adsorption sites, b. the molar fraction of nitrogen monoxide in the gases leaving the second catalyst for selective reduction of nitrogen oxides is determined as a function of the molar fraction of nitrogen monoxide in the gases leaving the first catalyst for selective reduction of nitrogen oxides, and of the flow rate in the second catalyst for selective reduction of nitrogen oxides, as well as of a sixth temperature-dependent 1D mapping in the second selective nitrogen oxide reduction catalyst and a seventh flow-dependent 1D mapping in the second selective nitrogen oxide reduction catalyst.

4. Estimation method according to claim 2 or 3, in which the maps are calibrated according to measurements made during tests.

5. Estimation method according to claim 1, wherein the polluting species are carbon dioxide CO^, carbon monoxide CO, hydrocarbons HC, ammonia, nitrogen monoxide NO, nitrogen dioxide or nitrous oxide N2O,

6. Motor vehicle equipped with an estimation system configured so as to carry out the estimation method according to any one of claims 1 to 5, in particular within an on-board diagnosis.

7. Motor vehicle according to claim 6, further comprising a partial recirculation circuit of the exhaust gases at the intake.